1. Field of the Invention
The present invention relates to a signal processing unit configured to communicate with a RFID tag which can write in and read out information via radio communication.
2. Description of the Related Art
A RFID (Radio Frequency Identification) system configured to read out information from a small-sized RFID tag (responder) in which predetermined information is stored by a predetermined apparatus for communicating with a RFID tag (signal processing unit) contactlessly is known. Since this RFID system is capable of reading out the information stored in the RFID tag through communication with the apparatus for communicating with a RFID tag even if the RFID tag is stained or positioned in a hidden position, practical use in various fields such as merchandize control, inspection process and the like is expected.
As one of radio communication systems using a RFID tag which begins to be utilized in various fields as above, there is known an apparatus for communicating with a RFID tag configured to read out or write in information from/to a RFID circuit element (IC tag) via radio communication. In communication between this apparatus for communicating with a RFID tag and a RFID tag, there is a trouble in which favorable communication is obstructed by influence of transient response. Thus, an art to suppress such an influence of the transient response is proposed. For example, an interrogating machine for data carrier described in JP, A, 2001-53642 can be cited. According to this prior art, a signal waveform is received by a pseudo data carrier, the received signal waveform and a predetermined response waveform expected from transmission data are compared, and by applying feedback to a driving level of a transmission coil so that an error portion of the comparison result is modified, the influence of the transient response involving conversion of the signal from the interrogating machine can be reduced and favorable communication can be realized.
As another example of the apparatus for communicating with a RFID tag, for example, is also proposed as described in JP, A, 2006-79217. In this apparatus for communicating with a RFID tag, by transmitting an inquiry signal to a RFID circuit element and by receiving a response signal from the RFID circuit element present in a communication range, information reading or writing from/to the RFID circuit element is carried out. Also, this apparatus for communicating with a RFID tag is connected to a server through a network, and by accessing the server through the network using information (code information) read out of the RFID circuit element as a key, information of an article (target object) to which the RFID circuit element is attached is gotten.
As an influence of the transient response of a transmission modulation wave in the communication with a RFID tag by an apparatus for communicating with a RFID tag, a modulation degree of a transmission signal (interrogation wave) transmitted from the apparatus for communicating with a RFID tag is larger than that of a reply signal (response wave) returned from the RFID tag, and since a transient response period is overlapped with a return period of the reply signal from the RFID tag, a head portion of the reply signal is crushed by a wrap around signal from the transmission side, which is a trouble. In this case, in order to prevent the overlapping of the above periods, with regard to the signal by the transient response and the reply signal from the RFID tag, by processing one of them with priority while by suppressing the other processing, the overlapping should be able to be prevented. However, with the prior art described in the JP, A, 2001-53642, such consideration is not given and the trouble due to the influence of the transient response could not be solved. Thus, smooth communication has been prevented.
On the other hand, in the prior art described in the JP, A, 2006-79217, when a system is to be constructed, there is a need to newly install an apparatus for communicating with a RFID tag capable of network connection apart from an existing information terminal such as a personal computer. Particularly, if the network connection is to be made by radio communication, radio wave interference is caused by co-presence of the radio communication for the network and the radio communication with the RFID tag and smooth communication is prevented.